Field
The present disclosure relates to a reactor pressure vessel assembly including a flow barrier structure and/or a method of manufacturing the reactor pressure vessel assembly.
Description of Related Art
FIG. 1 is a cross-sectional view of a conventional natural circulation reactor pressure vessel assembly. FIGS. 2-4 are a plan view, a cross-sectional view, and a perspective view, respectively, of a portion of the reactor pressure vessel assembly in FIG. 1.
Referring to FIGS. 1-4, the reactor pressure vessel assembly 100 includes a housing H that surrounds a core inlet region 114, a shroud 104, a reactor core 112, a chimney assembly 108, and steam separators 118. The reactor core 112 is over the core inlet region 114. The chimney assembly 108 is between the steam separators 118 and the reactor core 112. The steam separators 118 are over the chimney assembly 108. The reactor core 112 may be defined by an inner surface of the shroud 104, a core plate 116 secured to a bottom of the shroud 104, and a top guide 120 secured to a top of the shroud 104. The shroud 104 may be a hollow cylindrical structure that separates the reactor core 112 from the downcomer annulus flow in the annulus A. The core plate 116 may support control rods and fuel assemblies that include a plurality of fuel rods in the reactor core 112. The top guide 120 may provide lateral support to the top of the fuel assemblies. The core plate 116 may support the control rods laterally. The control rods may be vertically supported by control rod guide housings that are welded to a bottom head in the reactor pressure vessel assembly.
The chimney assembly 108 includes a chimney barrel B, chimney partitions C, a chimney head CH, and a plenum 106. An inner surface of the chimney barrel B defines a space between the reactor core 112 and the steam separators 118. The plenum 106 is a portion of the space defined by the inner surface of the chimney barrel B between a lower surface of the chimney head CH and an upper surface of the chimney partitions C. A height of the plenum 106 may be about 2 meters, but is not limited thereto. The chimney partitions C are located inside the chimney barrel B. The chimney partitions C divide the space defined by the inner surface of the chimney barrel B into smaller sections.
The annulus A is defined by a space between an inner surface of the housing H and outer surfaces of the chimney assembly 108 (e.g., outer surfaces of the chimney barrel B) and reactor core 112 (e.g., outer surface of the shroud 104). Together, an inner surface of the chimney assembly 108 (e.g., inner surface of the chimney barrel B) and an inner surface of the reactor core 112 (e.g., an inner surface of the shroud 104) define a conduit for transporting a gas-liquid two phase flow stream from the reactor core 112 through the chimney assembly 108 to the steam separators 118.
The upward arrows in FIG. 1 indicate a flow direction of the gas-liquid two phase flow stream through the reactor core 112, chimney assembly 108, and steam separators 118. The chimney partitions C act to channel the gas-liquid two phase flow exiting the reactor core 112 into the chimney assembly 108 in order to limit cross flow and/or reduce the potential for recirculating eddies. The steam separators 118 may separate a gas portion of the gas-liquid two phase flow that flows through the steam separators 118 out a top of the reactor pressure vessel assembly 100, as indicated by the arrows above the steam separators 118 in FIG. 1. A remaining portion of the gas-liquid two phase flow that corresponds to the downcomer fluid from the steam separators 118 and steam dryer (not shown), referred to as separator downcomer flow, flows down from the top of the reactor pressure vessel assembly 100. The separator downcomer flow may come from two sources: a steam dryer (not shown) and a return from the steam separators 118. A substantial portion of the separator downcomer flow (e.g., about 97%) may come from the return flow of the steam separators 118 and a comparatively smaller portion (e.g., about 3%) of the separator downcomer flow may come from the steam dryer (not shown). However, the relative contributions to the separator downcomer flow from the return flow of the steam separators 118 and the steam dryer (not shown) are not limited to about 97% and about 3%, respectively, and may be different depending on operation conditions and/or variations in design. FIG. 3 illustrates a fluid level L of the separator downcomer flow, but the fluid level L of the separator downcomer flow may vary from the fluid level L indicated in FIG. 3 depending on operation conditions.
The reactor pressure vessel assembly 100 includes at least one feedwater sparger 126 in the housing H that is configured to deliver a sub-cooled feedwater into the annulus A. Each feedwater sparger 126 is connected to a corresponding feedwater opening defined by the housing H. The reactor pressure vessel assembly 100 may include a plurality of feedwater spargers 126 arranged in a circular pattern over the chimney assembly 108 and connected to a plurality of feedwater openings defined by the housing H. The housing defines a feedwater opening for each feedwater sparger 126. The annulus A is in fluid communication with the feedwater opening connected to the feedwater sparger 126 and the conduit for transporting of a gas-liquid two phase flow stream from the reactor core 112 through the chimney assembly 108 to the steam separators 118.
As shown in FIG. 3, a support plate 128 may be arranged a distance H1 above the chimney head CH, but below a height of the feedwater spargers 126. The support plate 128 may be secured to the chimney head CH. For example, the support plate 128 may be welded to the steam separator stand pipes SP. Chimney head bolds (not shown) may fit inside the support plate 128 through slip fit holes. The support plate 128 may support the outer stand pipes, and may support the chimney head bolts, laterally. The support plate 128 may have a ring structure with a width W1. From a plan view, as shown in FIG. 2, the feedwater spargers 126 expose the width W1 of the support plate 128 below. The steam separators 118 are over an area surrounded by the support plate 128, but the steam separators 118 may be arranged so they are not directly over the support plate 128 in a vertical direction. In other words, as shown in FIG. 2, the support plate 128 may surround the steam separators 118 in a plan view. As shown in FIG. 4, even though some of the outer steam separators 118 may be on top of stand pipes SP that partially contact the support plate 128, the steam separators 118 are not directly over a portion of the support plate 128 in a vertical direction. As shown in FIG. 4, only part of the circumference of the outer stand pipes SP is in contact with support plate 128 where the outer stand pipes intersect the support plate 128.
As indicated by the down arrows in the annulus A of FIG. 1 and the arrows in the core inlet region 114 of FIG. 1, the sub-cooled feedwater may flow down the annulus A through the core inlet region 114 into the reactor core 112. The arrows in FIG. 3 illustrate part of the separator downcomer flow may be redirected to flow around the feedwater sparger 126 and the support plate 128 into the annulus A. The mixture of the sub-cooled feedwater flowing in the annulus A with the portion of the separator downcomer flow that is redirected into the annulus A may be referred to as the annulus downcomer flow. In the reactor core 112, fuel rods may heat the annulus downcomer flow received from the core inlet region 114 and the portion of the separator downcomer flow received from the top of the reactor pressure vessel assembly 100 to provide the gas-liquid two phase flow stream that flows upward from the reactor core 112 through the chimney assembly 108 to the steam separators 118.
Complete mixing (and/or a desired level of mixing) between the separator downcomer flow and the sub-cooled feedwater does not occur. All (or substantially all) separator downcomer flow may be directed into the annulus A; however, at least a portion of the separator downcomer flow may bypass the sub-cooled feedwater and avoid mixing or reduce a degree of mixing. In the conventional natural circulation reactor pressure vessel assembly 100, there is incomplete mixing of the separator downcomer flow and the sub-cooled feedwater before delivery to the reactor core 112. A temperature of the sub-cooled feedwater is generally less than a temperature of the separator downcomer flow. Consequently, the incomplete mixing between the separator downcomer flow and sub-cooled feedwater may cause temperature variations into the fuel rods and supports for the fuel rods in the reactor core 112. Accordingly, improved mixing between the separator downcomer flow and sub-cooled feedwater before entry into the reactor core 112 is desired.